The isolated rat liver, routinely perfused for 24 hours with bovine red cells in Krebs-Ringer bicarbonate buffer containing 3% bovine serum albumin, will be used to extend earlier studies, seeking to define hormonal factors regulating net synthesis of specific plasma proteins. To be studied singly and as supplements to insulin and cortisol will be the hormones prolactin, histamine, serotonin, prostaglandins E1, E2, F1 alpha, and F2 alpha, Beta-estradiol and testosterone. In addition to albumin, fibrinogen, alpha1-acid glycoprotein, alpha2-macroglobulin, and haptoglobin, net synthesis of the proteins alpha 1-macroglobulin, antithrombin III, alpha 2-HS globulin, hemopexin and ceruloplasmin will be measured. Mechanisms of altered synthesis will be examined in terms of changes in the levels of specific mRNAs for the proteins.